Fixed-Path Length Laser-Induced Sound Pinging: A Streamlined Method for Sound Speed Determination in Arbitrary Liquids

Abstract

Recently, we introduced laser-induced sound pinging (LISP) as a simple photoacoustic technique for the expedient and fairly rapid (2–3 min) measurement of the speed of sound traversing low-volume samples (25–1000 μL), built around an inexpensive tattoo-removal laser source (Sens. Actuators B-Chem. 2019, 291, 401–410). In this report, we expand on the utility of this technique by improving the facility of measurement and speed of analysis by adopting a fixed-path length (FPL) architecture which allows for much faster analysis (1–5 s) of similar sample volumes. The FPL-LISP setup was employed to determine the speeds of sound at temperatures from 293 to 333 K for four popular hydrophilic deep eutectic solvents (DESs) containing choline chloride (i.e., reline, ethaline, glyceline, and maline), plus several representative decanoic acid–based (i.e., hydrophobic) DESs. The temperature-dependent speeds of sound were used alongside the corresponding experimental densities to calculate the bulk modulus for these il...